Use `ConnectError.unavailable` when client is offline #804

Job	Run time
build-eliza-cocoapods-example	55s
build-library-macos	1m 56s
build-library-ios	1m 55s
build-eliza-swiftpm-example	1m 33s
build-library-watchos	1m 24s
build-plugin-and-generate	1m 4s
run-conformance-tests	2m 36s
build-library-tvos	1m 47s
run-unit-tests	1m 53s
validate-license-headers	17s
run-swiftlint	10s
	15m 30s

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